1. Field of the Invention
This invention relates to systems for modulating and scanning multi-chrominant light beams, particularly laser beams, using a reversing scanning mechanism to provide successive line scans of color-modulated information.
2. Description of the Prior Art
In a system in which a modulated light beam is to be displayed in raster fashion, such as in a conventional TV display, it is known to use a galvanometer driven or other reciprocating type of reflective scanning mechanism to provide successive horizontal line scans. The horizontal line frequency in accordance with presently existing television standards is 15,750 cycles per second, which can be satisfied, for individual line scans, by a galvanometer, torsion drive or other high speed type of drive. However, the return time between successive lines in the television standard is based upon the flyback time of an electron beam, and is far less than the time required for a reciprocating mechanism to return from the end of its forward scan motion to the start of the next scan. Thus many workers in the art have proposed the use of, or have actually employed, other scanning mechanisms such as multi-sided prisms or acousto-optic scanners. These, however, are substantially more complex and costly than the reciprocating mirror type of system, and also may introduce unwanted light losses into the transmitted beam. It has therefore been suggested, in U.S. Pat. No. 3,614,312 to Fournier et al, Oct. 19, 1971, that a pair of oppositely oscillating mirrors can be utilized, and that a light switch can be utilized to deflect the beam alternately to the mirrors, so that each horizontal scan line is scanned by a different mirror, with the beams then being recombined into the desired optical path. This substantially complicates the optical path, however, and in fact more than two oscillating scanners may have to be used, as disclosed by Fournier et al. In addition, nonlinearities in the mirror motion must inherently be accepted by the system.